[RickPflimlin]

Here is another ball source, though I haven't ordered from them.
They can get you very close to 2.38 mm chrome steel balls. They also have .093" size. Those look like they are 10 cents each. Part number 37432.

Bal-tec

$20.00 minimum order.

Thank you very much. I'll put in an order and I don't mind having extras to make the $20.00 minimum.

[philbur]

If it were worn balls it would produce backlash not the incremental offset you are getting. A worn screw thread would produce incremental offset. 3000 hours is not necessarily a lot of hours but it would be if it's all at the same position on the table/ballscrew.. If the problem doesn't appear at large size text then this would suggest a very localised problem. Have you tried engraving at a different location on the table.

Have you tried switch the x/y drivers.

Just a few thoughts.

Phil

PS: Any theory will need to explain how/why the engraver manages to return to the start point with out any apparent offset?????

[mountaindew]

Finding the right sized balls to replace the ones in the ballscrews is now my biggest problem.

Didn't think this was possible. I understood these are complete assemblies and require complete replacement.
Can you replace just the balls or would these be matched and ground to the screw?

[TXFred]

Didn't think this was possible. I understood these are complete assemblies and require complete replacement.
Can you replace just the balls or would these be matched and ground to the screw?

I looked into this when I thought I had a bad ballnut. The ball returns aren't removable. They're closed off by a couple of pressed in plugs. If you could find a way to remove the plugs and replace them, then you could rebuild the ball nut.

And once you've replaced the balls, you would need to set the preload by making a new spacer to fit between the two ball nuts. This would require access to a lathe and a surface grinder.

Frederic

[RickPflimlin]

Have you tried engraving at a different location on the table?

Yes, 6 areas at all of the edges of the work area it's the same everywhere.

[popspipes]

Have you tried a regular rotary single flute engraving cutter to see what the results are?
A drag engraver is spring loaded and would have some clearance in the sliding mecanism, wondering if that may be causing the problem?

I dont understand why the characters seem to lean? I wonder if youve tried letters an inch tall to see if they lean as well?

[RickPflimlin]

I looked into this when I thought I had a bad ballnut. The ball returns aren't removable. They're closed off by a couple of pressed in plugs. If you could find a way to remove the plugs and replace them, then you could rebuild the ball nut.

And once you've replaced the balls, you would need to set the preload by making a new spacer to fit between the two ball nuts. This would require access to a lathe and a surface grinder.

Frederic

I replaced my Z ballscrew about a year ago and I took apart the old one and those plugs came out easily and go back in almost as easily. Maybe Tormach sources them from several vendors, or there is a difference between the 770 and 1100, newer/older? At that time I watched several videos of people rebuilding them. It seemed easy enough but I'll need to rewatch them to see what they were saying about peload.

My main concern at this point is the ball size. The last link that was posted on ball size shows balls .0927 - .092823 - .093 - .093038 - .0932 - .09321 - and so on. I don't have the ability to measure that closely and since my balls are worn any measurement would be compromised.

So the next question is about who could rebuild them to original specs?

[RickPflimlin]

Have you tried a regular rotary single flute engraving cutter to see what the results are?
A drag engraver is spring loaded and would have some clearance in the sliding mecanism, wondering if that may be causing the problem?

I dont understand why the characters seem to lean? I wonder if you've tried letters an inch tall to see if they lean as well?

I have been engraving on the 770 for over three years with every combination of bits and holders there are. The drag bit is my main one but I have used others as recently as a couple weeks ago, and I did try 3 different drag holders. This problem just showed up a week to 10 days ago. Or at least it got noticeable in that time?

I have engraved taller letters with no noticeable lean but I will try the G0 combination that shows the lean the worst at 1 inch tall.

[RickPflimlin]

Didn't think this was possible. I understood these are complete assemblies and require complete replacement.
Can you replace just the balls or would these be matched and ground to the screw?

There are many companies that offer rebuilding services but to what specs? Who to pick?

[popspipes]

How is the work held on the machine? Maybe sone flex in fixturing as in tape etc?
Just grasping at straws???

[RickPflimlin]

Held very tightly in a vise.

Here are the letters that leaned the worst at 1/10 of an inch 1 inch tall. I can't see any lean but there is clearly a disconnect where the engraving bit meets up. I'm sure that's the .007-.008 of backlash.

[popspipes]

Have you tried an indicator in the vise against the side of the engraving tip to see how much the holder can actually flex just pushing it with a finger right then left? A lot of stickout would make a big difference too.

[RickPflimlin]

Have you tried an indicator in the vise against the side of the engraving tip to see how much the holder can actually flex just pushing it with a finger right then left? A lot of stickout would make a big difference too.

I think three+ years of not having a problem, testing with three different engravers, and the fact that I have .007-.008 of X backlash along with everything already talked about brings this down to a backlash problem. I have adjusted my gibs, and tightened my thrust bearings. I can only see the ballscrew or the screws holding the ballscrew pillow block as being where the backlash is coming from?

I was just able to move the table all the way to the right and get a wrench on the ball nut carrier. All bolts are tight.

Does anyone have any experience with a Ballscrew rebuilder that they recommend? I will buy new ones but I would like to have the others rebuilt for backups.

[RickPflimlin]

This all brings up the subject of a backup machine. Are the C7 ballscrews on the 440 up to doing good engravings down to .0625?

[MichaelHenry]

I read about someone else having that problem and wished I had checked when I had all the guards and covers off.

I will check that out but I will have a replacement on hand before I tear it down that far again. Maybe I can fish a long extension in there and check them?

Only if you are a lot more dexterous and patient than I am. Getting to those SHCS really isn't that bad though unless your table is fully loaded and the mill is in a really cramped space.

So far as replacing ball nut balls goes, a new lead screw is $600, which doesn't seem too bad as such things go.

[mountaindew]

There are many companies that offer rebuilding services but to what specs? Who to pick?

The machine would set un-used while you send this off to be rebuilt. With shipping on stuff these days it could be days to weeks "I would go nuts". Also buying parts then taking machine apart and sending off to be rebuilt sounds complicated. I would as mike notes above buy a new assembly for axis in question. Have on hand to do replacement at a convenient time and hopefully enjoy the new found accuracy.

[RickPflimlin]

The machine would set un-used while you send this off to be rebuilt. With shipping on stuff these days it could be days to weeks "I would go nuts". Also buying parts then taking machine apart and sending off to be rebuilt sounds complicated. I would as mike notes above buy a new assembly for axis in question. Have on hand to do replacement at a convenient time and hopefully enjoy the new found accuracy.

My plan is to buy a new one and the have the old ones rebuilt as backups. I'm already worried about the Z ballscrew that I replaced about a year ago. The Z will get noisy from time to time. I find that between engravings if I zip it up and down the length of the ballscrew it will quiet down. That can't be good.

[LeeWay]

You don't ever want to hear noise out of a ball screw.

[mountaindew]

My plan is to buy a new one and the have the old ones rebuilt as backups. I'm already worried about the Z ballscrew that I replaced about a year ago. The Z will get noisy from time to time. I find that between engravings if I zip it up and down the length of the ballscrew it will quiet down. That can't be good.

Wow,
Do you have an auto oiler? Have you checked all the way lube lines and visually see each screw is getting some lube?
I run my machine a great deal and put some loads on it at times that would induce wear a number of times faster then engraving with no wear problem.
Anyway hope you zero in on the results your looking for. I get excellent accuracy on all axis not just 2d scratches on surface

[RickPflimlin]

Wow,
Do you have an auto oiler? Have you checked all the way lube lines and visually see each screw is getting some lube?
I run my machine a great deal and put some loads on it at times that would induce wear a number of times faster then engraving with no wear problem.
Anyway hope you zero in on the results your looking for. I get excellent accuracy on all axis not just 2d scratches on surface

Oil is not the problem. All the oilers are working fine and if anything I over oil. When my Z ballscrew went out the oil just shimmered with chrome flakes.